This invention relates in general, to heat exchangers; and, in particular to apparatus for decreasing noise and vibration in the heat exchanger.
One application of the present invention occurs in combination with a heat recovery steam generator (HRSG), an example of which is shown in U.S. Pat. No. 3,934,553 assigned to the assignee of the present invention. The HRSG is a free standing duct which defines a hot gas flow path in combination with a plurality of discrete tube bundles which contain a fluid to be heated and between which a non-contact heat exchange relationship occurs. The HRSG may be connected to the exhaust end of a gas turbine which provides a source of hot gas. If the tube fluid to be heated is water for eventual input into a steam turbine, the combination may be termed a combined cycle power plant. Alternatively and without limitation, the present invention may be applicable to any type of non-contact heat exchanger wherein gas is passed through tube bundles.
It has been found that at certain gas velocities through an enclosed gas duct a loud resonance will occur. In the context of a multi-tube bundle HRSG of a combined cycle power plant, as load changes are made with respect to the gas turbine, resonant noise may occur which is objectionable to the surrounding community. The acoustic resonance may also excite large amplitude lateral vibrations of the duct walls or tubes if the frequency of acoustic oscillations happens to be close to the natural frequencies of the structures.
The stimulus to the noise is the hot gas flow which changes velocity as load changes are made on the gas turbine. The response is the HRSG environment including duct width perpendicular to the gas flow and general axial orientation of the HRSG tube bundle. Other factors to be considered are the temperature gradiant within the HRSG and other physical parameters within the HRSG.
One solution of the excessive noise problem lies in dealing with the response. In other words, the response noise occurs at a particular frequency which may be altered by changing a physical parameter of the gas duct. For example, detuning baffles could be inserted between tube bank rows and hence shorten the cross section dimension of the duct. This would raise the response frequency away from the stimulus frequency. The objection to this solution is that it creates an obstruction to gas flow as well as to certain accessories such as sootblowers and often times is impossible to install at ideal locations. Hence, while viewed as one available solution the use of detuning baffles is far from an ideal solution or even a universal solution.